As you know, I don't do it and Michelle Bridges (who's plan I'm following) tells us not to do it. It's not very productive to losing weight IMO. I survive on a 1200 cal diet with 500cals exercise per day and I've not once been ill, injured or felt so ridiculously out of energy that I've needed to eat more. May be different for different people though (and I will carb load to an extent before a long run - like before my 15km fun run last year, I had pasta for lunch the day before).